Radio noise filter

ABSTRACT

In a radio noise filter a capacitor, arranged in a capacitor casing having insulating end pieces carrying the input and output terminals of the filter, is to be combined with a pair of choke coils, which, due to heat dissipation, should be arranged outside the casing. As the choke coils are mechanically weak they cannot themselves carry terminals to be connected to the external wiring. Therefore, two auxiliary terminals are provided in each of the end pieces and the choke coils are connected between these auxiliary terminals which are furthermore connected to the input and output terminals of the filter in any suitable manner.

United States Patent 1 Lykke Oct. 16, 1973 RADIO NOISE FILTER 3,267,396 8/1966 Scott 333/79 x l h [76] Inventor: Gravs Larsen Lykke, No. 2939095 960 C wok 333/79 x Ledagersn vanlose Denmark Primary Examiner-Eli Lieberman [22] Filed: July 8, 1971 Assistant Examiner-Saxfield Chatmon, Jr. [21] Appl. NO: 160,667 Attorney-Richard C. Sughrue et al.

[57] ABSTRACT Foreign Application Priority Data J I 13 1970 D 3640 In a radio noise filter a capacitor, arranged in a capacenmar itor casing having insulating end pieces carrying the input and output terminals of the filter, is to be comg 333/79 333/ gii bined with a pair of choke coils, which, due to heat d 79 70 s dissipation, should be arranged outside the casing. As le 0 care the choke coils are mechanically weak they cannot [56 R f Ct d themselves carry terminals to be connected to the ex- 1 I e erences le temal wiring. Therefore, two auxiliary terminals are UNITED STATES PATENTS provided in each of the end pieces and the choke coils 1,972,268 9/1934 Lesh 333/79 X are connected between these auxiliary terminals which 3,506,936 4/ 1970 L005 et al. 333/79 are furthermore connected to the input and output 2,221,105 11/1940 Otto 333/79 terminals of the fil in any Suitable manner. 2,163,775 6/1939 Conklin 333/79 2,073,880 3/1937 Robinson 333/79 X 7 Claims, 6 Drawing Figures PATENTEBHBT 16 I375 SHEET 2 OF 2 FIG. 5

FIG. 6

RADIO NOISE FILTER The present invention relates to a radio noise filter of the current lead-through type comprising a leadthrough capacitor or by-pass capacitor or capacitor combination accommodated in a casing, the two opposite ends of which consist of insulation material or have insulation pieces carrying input and output terminals for the current.

For reasons of safety, the two insulation pieces that carry the input and output terminals on noise filters of the type dealt with, have to be sufficiently strong so as to be capable of withstanding the mechanical influences from the input and output conductors and, in addition, they will have to be of an insulation material which ignites only with difficulty, such as bakelite, bakelite laminate or similar material.

Furthermore, such insulation pieces have to be carried or supported sufficiently securely so that they do not become detached when the filter is mounted or by influences from the input and output conductors of the apparatus to be fitted with the noise filter.

For noise filters consisting only of a capacitor or a capacitor combination, this does not give rise to any special problems since the end pieces carrying the terminals, in cases where the capacitor or capacitor combination casing consists of insulation material, may be constituted of portions of this casing and, in the case where a portion of the casing is of metal, be carried by the metallic portion of the casing.

In the case of filters containing, in a known manner, a pair of choke coils, it has hitherto been difficult to achieve a simple and yet, from a safety standpoint, secure mounting of the choke coils which, due regard being had to heat dissipation, should be mounted outside the capacitor or capacitor combination casing and which, in order to obtain the requisite self-induction,

- are wound on to cores of ferrite or, by way of example,

bakelized iron powder, the mechanical strength of which is insufficient for them to have one end unsup ported, let alone to carry a terminal on this end.

Holders intended for collectively carrying several electrical components are known, but such holders, in their known form of construction, are incapable of safeguarding mechanically weak components against mechanical influences acting upon components andv holders. Moreover, their function requires them to be of insulation material and their complicated shape precludes their being fashioned by any methods other than moulding or pressing in materials of which thermosetting ones are the most suitable from a point of view of safety, for which reason their production is relatively slow and their production costs correspondingly high.

These drawbacks are eliminated according to the invention by each of the insulating end pieces of the capacitor being provided with two auxiliary terminals, between which'two-choke coils are arranged and which are connected to the main terminals in such a way that the choke coils are, in a known manner, electrically sit-' uated between the input terminals of the noise filter and the capacitor or capacitor combination. Hereby it is achieved that it is possible to fit the choke coils outside the capacitor casing with the supply conductors securely fixed and without their being affected by extraneous mechanical forces.

The choke coils may be secured solely by means of the supply conductors or the noise filter may, in conformity with an embodiment according to the invention,

have a plurality of resilient tags for mechanically securing the choke coils on the capacitor or its securing means. I v

In the following, the invention is explained in greater detail with reference to the accompanying, schematic drawings, in which FIG. 1 shows an electrical circuit diagram with a noise filter according to the invention,

FIG. 2 shows a noise filter according to the invention in side elevation,

FIG. 3 shows the same noise filter seen from one end,

FIG. 4 shows the same noise filter seen from the end after the removal of certain components,

FIG. 5 shows a longitudinal section through the noise filter, and

FIG. 6 shows a section of the capacitor of the noise filter including a conductor in contact with one of the capacitor electrodes.

In FIG. 1, an electromotor M is shown which, via a noise filter capacitor C and two choke coils D is connected to mains terminals N, possibly via a switch (not shown). Besides the main electrodes, the capacitor contains an auxiliary electrode that is connected to the capacitor casing which is indicated by a dotted curve.

The noise filter shown in FIGS. 2-4, which comprises those components which in FIG. 1 are indicated inside the rectangle denoted with S, has a cylindrical capacitor casing 1, in which a capacitor winding 2 is mounted. Around the capacitor, a metal strip 3 is fitted, the ends of which are bent over, welded together and provided with a hole 4 which can be utilized when securing the noise filter on an electrical machine. Around the capacitor casing, at-each of its ends, a cover 5 and 6, respectively, of insulation material is fitted. In FIGS. 2 and 4, cover 6 has been omitted so as to provide a clear view. On each of covers 5 and 6, two projections 7,8 and 9,10, respectively, are arranged which terminate in resilient tags gripping around two choke coils 11 and 12 and thereby securing them.

The ends of capacitor casing l are closed by discs of insulation material. Only one of these discs, 13, is'visible in the drawing. Each of the discs incorporates two contact spaces 14 and 15, as well as two soldering-flaps 16 and 17. Covers 5 and 6 are provided with apertures 18-21, through which spades l4 and 15 and soldering flaps l6 and 17 project. Moreover, covers 5 and 6 are provided with various projections and partitions 22-24, which are intended to ensure the necessary insulation between live parts.

Referring to FIGS. 2 and 5, those contact spades 14a and 15a which project over the end of the capacitor shown on the right-hand side of FIG. 2', and 5 are connected to two conductors 25 and 26 extending through capacitor winding 2 and which project from its'lefthand end and which, in their passage, each make contact with one ofthe capacitor electrodes 1 as more clearly shwon in FIG. 6. In FIG. 6, one of the capacitor electrodes is designated 30 and the other one 31, whereas the insulation between the electrodes is designated 32. The flat part of conductor 26 is shown in contact with the electrode 30. Those portions of wires 25 and 26 which are located in the capacitor winding may tend to the right-hand end of the capacitor where they are connected to the two soldering flaps 16a, 17a. Finally, soldering flaps l6 and 17 in insulation disc 13 at the left-hand end of the capacitor are connected to contact spades 14 and 15 mounted in the same disc. The circuit shown inside rectangle S of FIG. 1 is hereby brought into being.

Soldering flaps l6 and 17 are expedient elements for establishing a connection to the choke coils. Projections 7-10 and the associated tags may be dispensed with, and the choke coils can be held solely by means of their supply conductors. in this case in particular will the soldering flaps be of relevance.

Wires 27 and 28 need not connect the left-hand ends of wires 25 and 26 to the soldering flaps at the righthand end of the capacitor, but can, instead, connect the soldering flaps at the right-hand end to the contact spades at the left-hand end, in which case wires 25 and 26 have to be connected to the soldering flaps at the left-hand end. There is no need for wires 27 and 28 to extend through a central hole in the capacitor winding, but they can be located outside same, possibly outside the capacitor casing. Wires 25 and 27 can be made up of one through wire. The same applies to wires 26 and 28.

As can be seen, in the embodiment shown in FIGS. 2-4 no direct connection exists from the capacitor winding to the terminals and soldering flaps in the lefthand end of the capacitor, as the connection to these contact means passes through the choke coils located outside the capacitor casing. With this embodiment it is consequently possible to use, for instance, a coldpressed cup with a sealed bottom in the left-hand end as capacitor casing. in this case, insulation disc 13 acquires the character of a dummy cover and serves merely as a carrying means for the terminals and soldering flaps in this capacitor end.

In the present case, where the capacitor is combined with two choke coils, the capacity of the capacitor winding is to all intents and purposes determined by the radio noise attenuation desired for the lower radio fre quencies, while the self-induction of the choke coils is of particular importance for the attenuation of higher frequencies. The requisite capacity and self-induction values consequently depend upon the noise intensity and noise spectrum of the radio noise source. In actual practice it is not necessary in every case, in order to achieve satisfactory noise attenuation, for the capacitor to be a lead-through capacitor. There is then no need for connections 27 and 28 in the capacitor shown in FIGS. 2-4 to be passed from wires 25 and 26 in the lefthand end of the capacitor to the soldering flaps in its right-hand end, but they may be in the formof short wires between the terminals and soldering flaps in the right-hand end of the capacitor.

The invention is not restricted to the embodiments described in the foregoing and shown in the drawings,

type, including a capacitor element surrounded by a cylindrical casing, said casing including insulation material, at least one choke coil positioned external to said casing and having one end connected to said capacitor element, connection terminals firmly anchored in said insulation material for connecting said choke coil and the capacitor element to conductors, external to said casing, the improvement comprising;

holding means for maintaining said choke coil in position outside said casing, and

auxiliary terminals firmly anchored in the insulation v material and connecting said choke coil to said connection terminals.

2. The noise filter of claim 1 wherein a first auxiliary terminal electrically connects the other end of said choke coil to a first connection terminal and a second auxiliary terminal connects said one end of said choke coil to said capacitor element, said capacitor element being further connected to a second connection terminal.

3. The noise filter of claim 2 further including a second choke coil, additional holding means for maintaining said second choke coil in position outside said casing, third and fourth connection terminals and third and fourth auxiliary terminals anchored in said insulation material, said third auxiliary terminal electrically connecting said third connection terminal to one end of said second choke coil said fourth auxiliary terminal electrically connecting the other end of said second choke coil to said capacitor element, said capacitor element being connected to said fourth connection terminal.

4. The noise filter of claim 3 wherein said capacitor element comprises a wound capacitor having a central hole and two lead through conductors extending through said hole and electrically insulated form each other, said lead through conductors being electrically connected to said second and fourth auxiliary conductors respectively and said capacitor element.

5. The noise filter of claim 2, wherein said holding means includes resilient tabs for clamping and holding the choke coils.

6. The noise filter of claim 4 further including insulation covers disposed over said discs of insulating material.

7. A radio noise filter of the type comprised of a capacitor element encased in a protective casing said casing including insulating material and choke coils situated external to the casing and electrically connected to said capacitor element and additional circuitry through connection terminals anchored in said insulating material, the improvement comprising,

auxiliary terminals, in addition to said connection terminals, anchored in said insulating material sad electrically connecting said choke coils to said connection terminals and the capcitor element, and holding means, including resilient taps, for maintaining the choke coils in position outside the cas- 

1. A radio noise filter of the current lead through type, including a capacitor element surrounded by a cylindrical casing, said casing including insulation material, at least one choke coil positioned external to said casing and having one end connected to said capacitor element, connection terminals firmly anchored in said insulation material for connecting said choke coil and the capacitor element to conductors, external to said casing, the improvement comprising; holding means for maintaining said choke coil in position outside said casing, and auxiliary terminals firmly anchored in the insulation material and connecting said choke coil to said connection terminals.
 2. The noise filter of claim 1 wherein a first auxiliary terminal electrically connects the other end of said choke coil to a first connection terminal and a second auxiliary terminal connects said one end of said choke coil to said capacitor element, said capacitor element being further connected to a second connection terminal.
 3. The noise filter of claim 2 further including a second choke coil, additional holding means for maintaining said second choke coil in position outside said casing, third and fourth connection terminals and third and fourth auxiliary terminals anchored in said insulation material, said third auxiliary terminal electrically connecting said third connection terminal to one end of said second choke coil, , said fourth auxiliary terminal electrically connecting the other end of said second choke coil to said capacitor element, said capacitor element being connected to said fourth connection terminal.
 4. The noise filter of claim 3 wherein said capacitor element comprises a wound capacitor having a central hole and two lead through conductors extending through said hole and electrically insulated form each other, said lead through conductors being electrically connected to said second and fourth auxiliary conductors respectively and said capacitor element.
 5. The noise filter of claim 2, wherein said holding means includes resilient tabs for clamping and holding the choke coils.
 6. The noise filter of claim 4 further including insulation covers disposed over said discs of insulating material.
 7. A radio noise filter of the type comprised of a capacitor element encased in a protective casing said casing including insulating material and choke coils situated external to the casing and electrically connected to said capacitor element and additional circuitry through connection terminals anchored in said insulating material, the improvement comprising, auxiliary terminals, in addition to said connection terminals, anchored in said insulating material and electrically connecting said choke coils to said connection terminals and the capacitor element, and holding means, including resilient taps, for maintaining the choke coils in position outside the casing. 